The invention relates generally to a seat such as a seat for use in a motor vehicle, more specifically a seat which includes an adjustable back support arrangement.
Seats such as those fitted in motor vehicles are often provided with back support arrangements which are adjustable in respect of depth, that is to say, in the direction of the thickness of the upholstery of the backrest portion of the seat, while the position of the support effect, in respect of the height or generally vertical extent of the backrest portion of the seat, is fixed and predetermined. However, as will be readily appreciated, people do not all have the same kind of spinal column nor do they all have the same need for support at a given location. Thus, it may be found that support is required for the occupant of a seat, not only with a different depth or extent of forward projection of the support arrangement, but also at a different height, if the support arrangement is to provide the optimum form of support, from a medical point of view. In addition, even when considering one and the same type of spinal column, it is desirable to be able to alter the loading on the intervertebral discs in order to avoid permanently loading individual discs, with all the harmful consequences that that may entail.
The above-discussed problems are particularly important from the point of view of drivers of commercial vehicles who often have to spend for example up to eight hours per day, or even longer, in a sitting position.
Laid-open German application (DE-OS) No. 30 45 809 (U.S. Ser. No. 06/325,496 filed 11-27-81 now U.S. Pat. No. 4,425,910) to the present applicant discloses a seat having a backrest with an adjustable vertebral support, which is integrated in the backrest portion of the seat. That seat has two separate adjusting elements, in the form of curved spring plate members, which are adjustable in respect of the depth of the backrest cushion and which are disposed one above the other in the heightwise direction of the backrest. The two spring plate members which are actuable by a suitable actuating arrangement engage a common, curvable support plate which is disposed at the rear of the backrest cushion or upholstery. That seat and back support arrangement provides for adjustment both in respect to the depth of the backrest and also in respect to the heightwise direction of the backrest, by virtue of having the two separate spring plate members, with a suitable mechanism for separately curving the two spring plate members as required.